Underwater vibration analysis method for rotating propeller blades using laser Doppler vibrometer

Abstract

Vibration analysis for rotating propeller blades under water is obviously challenging. This study proposes stationary and tracking laser Doppler vibrometer (LDV) based measurement techniques for vibration analysis of the rotating propeller. The vibration measurement setup consists of an LDV, a DAQ and control system, and the rotating propeller that contains five blades mounted to the shaft through a rotor. To confirm the reliability of the proposed stationary and tacking LDV measurement results, the hammer impact tests are performed using a contact PZT accelerometer to obtain the velocity vibration results in time and frequency domain. These results are compared with LDV measurements for both in air and underwater cases. Both LDV and contact PZT measurements were taken simultaneously. The compared results show that the time-velocity signals and the corresponding frequency components obtained using hammer impact tests are very similar to the proposed LDV based measurement techniques. In addition, a numerical simulation is performed using COMSOL Multiphysics software to obtain natural frequencies of the system in air and underwater cases. These numerical simulation results are compared with bolt impact measurements taken on rotating propeller blade using LDV. Comparison of stationary and tracking LDV measurement results with the numerical analysis for in air and underwater cases showed matching results. From these results, it is concluded that the proposed techniques can be effectively used for underwater vibration measurement of the blades of rotating propeller.